BRA researchers in Berlin-Dahlem would improve this method and convert it into the standard procedure for testing varieties for wart resistance from 1930 on. Köhler and Lemmerzahl, building also on work from Mary D. Glynne at the British Rothamsted Experimental Station, replaced the winter sporangia with summer sporangia obtained from warted tissues collected from infected potatoes. By inoculating summer sporangia directly into the tuber sprouts, ideally when the sprouts were about 2 millimeters long, infections were detected already after 4 hours of inoculation. This so-called Glynne-Lemmerzahl method not only saved a considerable amount of time; it also made it possible to circumvent the use of large amounts of wart compost, which the previous method had required. It also required much less laboratory space. By 1929 the BRA had tested resistance to wart disease in about 10,000 breeding lines, a number that would climb to 30,000 in 1936 and that justified every effort to streamline inoculation procedures.[34]
Success in identifying susceptibility to wart would make resistance to that disease an exemplary case for a cleansing of the seed market. Through application of the Glynne-Lemmerzahl method on a grand scale, non-resistant varieties were to be eliminated from the German fields. As has already been mentioned, potato farmers had about 1,500 varieties at their disposal by the end of the 1910s.[35] The launching of Varietal Registering Committees (Sortenregisterkomissionen) for potatoes shortly after the war by Appel in conjunction with the German Agricultural Society (DLG), an initiative not extended to cereals until 1927, was aimed at sorting out “original varieties” from cheap imitations as a way to reduce the number of varieties and allow farmers to make better-informed decisions.[36] In the 1920s the DLG began to distribute to its members an annual booklet of approved varieties. During the Nazi regime, that booklet would evolve into an official Imperial List of Approved Varieties (Reichssortenliste).
The research on wart disease had also led to an important development in the methodology for classifying potato varieties. The close attention to tuber sprouts demanded by the Lemmerzahl-Glynne method revealed their usefulness as markers of different varieties. Soon BRA researchers developed, parallel to the inoculation method, a new biological basis for establishing equivalence or distinction between varieties on the basis of observation of the form, size, and color of tuber sprouts—the so-called sprout test (Lichtkeimprüfung).[37] Before a commercial variety could make the list of approved varieties, it had to demonstrate its distinctiveness (Selbständigkeit) in relation to existent varieties. Before BRA researchers began to publish the list of varieties, seed merchants could simply cultivate other breeders’ creations, rename them, and sell them as their own at a cheaper price. Distinctiveness was based on characteristics (Merkmalen) such as color and form of the tuber and, after K. Snell’s work by the end of the 1920s, also on certain features of the sprouts.[38] But distinctiveness was not enough to gain entry to the list. A variety developed by a commercial breeder had also to possess interesting agronomic qualities (Eigenschaften) of yield, resistance, adaptability to different soils, color of pulp, or tuber form. To be on the list, potatoes had thus to pass through the standardized tests of the BRA that established their biological characteristics and agronomic qualities. In short, BRA researchers developed quick laboratory testing methods to guide commercial breeders’ work as well as to identify the varieties that should or should not be included in the list of approved varieties.[39]
The BRA and the RNS: The Streamlined Estate and the 1934 Seed Decree